Though it is not limited to this particular technical field, the invention relates to the field of beverage bottling, in which there is a constant need of maximum aseptic filling conditions, in order to minimize contamination of the liquid by external agents. Asepsis can become a critical issue, for example in the case of milk bottling, and especially in raw milk bottling.
The design of filling machines must ever find a compromise between production rate and asepsis.
Production rates, on the one hand, require that the liquid be supplied with maximum flow rate to the container.
For example, EP 1 310 454 discloses a valve unit comprising a hollow body in which a plug is slidingly mounted and a guide means for the plug, a passage being formed in the hollow body for a liquid. The valve plug is integral with a piston associated to a pressurization chamber. Introduction of compressed air at a sufficient pressure in the pressurization chamber raises the piston to put the lug in an open state, thereby allowing the filling liquid to be supplied in the container. In such a structure, liquid flow rate depends upon the elevation height of the piston during the filling operation.
In theory, in order to maximize the flow rate, the piston should be elevated at the maximum height.
But, on the other hand, asepsis requires that the environment of the container be as clean as possible. In particular, splashes and overflowing should be minimized, for any droplet of liquid on the machine could become a substrate for bacterial development. This is why the filling liquid must, as far as possible, be supplied with great precision to the container.
In EP 1 310 454, the valve plug has a tip with a conical end portion having an ogival shape for guiding the liquid toward the mouth of the container. In addition, radial fins are provided on the valve plug in order to stabilize the liquid and avoid torsional movement thereof.
Although the fluid is supplied to the container in a laminar flow, turbulences appear when the level of liquid reaches the converging top portion of the container, in the vicinity of its neck. In order to avoid overflowing, a first common solution consists in limiting the liquid flow rate to minimize turbulences in the container. The main drawback of such a solution is that it unquestionably affects the production rates. A second solution consists in stopping the filling when the level of liquid is at a sufficient distance from the neck. This solution has two main drawbacks. First, the container needs to be over-dimensioned, which is material consuming. Second, there is in the filled container an important overlying volume of air, resulting in the customer thinking that the container is under-filled and therefore turning to another supplier. This is why the first solution is often preferred, despite its bad consequences on the production rates.